Adsorbents for a variety of purposes have been developed. These include carbon materials for organic species, alumina of various phases for acid gases and selected organics, silica adsorbents for water, natural and synthetic molecular sieves (including zeolites) for general adsorbent applications, and ion exchange resins for hydrocarbons and oxygenated organics as well as acids and bases. The use of metal oxide systems other than silica, alumina, and molecular sieves, while having appeared frequently in the literature, is much less prominent in commercial applications.
U.S. Pat. Nos. 6,787,11815 and 6,458,741,16 as well as U.S. Patent pub. no. 20030166987,17 all by Roark, et al and commonly owned with the current application, teach materials and their use in selective destruction of CO, complete low temperature oxidation of volatile organic compounds, and destruction of organics in liquid media respectively. The materials taught are mixed metal oxides containing rare earth (Ce, La, or Gd) and transition metal oxides. In addition, the process and materials taught1 by Flytzani-Stephanopolous, et al in U.S. Pat. No. 5,242,673 are relevant. The materials, based on cerium oxide, are employed in a catalyst for the reduction of sulfur dioxide to sulfur using a reducing gas (e.g., CO). Materials disclosed herein, in contrast, contain a greater variety of elements and are not employed in a sulfur conversion process. An adsorbent catalyst containing Ce, Zr (or Ti), and Mn and other combinations of elements for capturing and destroying nitrogen oxides, hydrocarbons, and carbon monoxide is taught by Maunula in U.S. Pat. No. 6,818,582.2 U.S. Pat. No. 6,667,018, by Noda, et al, teaches a catalyst-adsorbent for purification of exhaust gases which can include a heat-resistant metal oxide based on a rare earth metal. Those materials, however, lack the multiplicity of species and functions or the materials of the present invention. Reactive metal hydroxide and metal oxide nanoparticles are taught by Koper, et al4 in U.S. Pat. No. 6,653,519. A rare earth metal is one such component of these materials. However, those materials are generally employed as disposable adsorbents or sorbents, in contrast to the adsorbent materials of the present invention. A method for reducing exhaust emissions from internal combustion engines is described in U.S. Pat. Nos. 5,916,129 and 5,687,565, by Modica, et al.5,8 Those patents disclose a sulfur oxide adsorbent which is comprised of an alkaline earth or zinc oxide along with a main group or transition metal oxide, or a rare earth metal oxide. U.S. Pat. No. 5,884,473, by Noda, et al,6 describes an adsorbent system for removal of nitrogen dioxide and hydrocarbons from exhaust in which the adsorbent contains oxides of alkali, alkaline earth, transition metal, and rare earth metals. Bhattacharyya, et al,7,9 in U.S. Pat. Nos. 5,750,020 and 5,591,418, disclose a metal oxide adsorbent comprised of a divalent metal (zinc or alkaline earth), a trivalent metal (including rare earths and transition metals), and vanadium, tungsten, or molybdenum. Materials disclosed and claimed herein, however, do not utilize such a combination of elements.
The combined removal of sulfur oxides, carbon monoxide, and nitrogen oxides from flue gas using an adsorbent which incorporates a cerium oxide promoter is disclosed in U.S. Pat. Nos. 5,591,417 and 5,458,861 by Buchanan, et al.10,11 Onitsuka, et al, in U.S. Pat. No. 5,439,868 teaches an adsorbent for removal of nitrogen oxides from gas streams which is comprised of metal oxides and halides.12 This is different from the disclosure herein in that metal halides are not employed as a constituent of the adsorbent. U.S. Pat. No. 4,917,875, by Moore, et al13 teaches alumina supported rare earth compounds as adsorbents for the removal of sulfur oxides from gases utilizing as cyclic adsorption-desorption process. Again, the materials disclosed are different from those disclosed herein. U.S. Pat. No. 4,869,735, by Miyazawa, et al,14 teaches a process utilizing an arsenic adsorbent which may contain oxides of alkaline earths transition metals, or main group elements. Disclosed herein, however, are adsorbents of markedly different composition.